Ultrasonic identification tags can be used to identify and inventory various products labeled with such tags, such as in a retail, factory, or warehouse environment. Ultrasonic identification tags generally transmit data modulated as a sequence of an ultrasonic carrier sound wave. The modulated data includes information, such as a serial number or other identification data, and/or product information, for example. An ultrasonic reader may then receive and demodulate the data from the ultrasonic sound wave, determining a presence of the product and the information about the product.
Typically, an ultrasonic tag is a relatively small device with its own enclosed power source or battery. Of course, producing ultrasonic signals requires power, and continually transmitting ultrasonic signals would quickly drain the battery. One way for the ultrasonic tags to conserve power is to not keep the transmitting emitter (transponder) powered at all times. When the tag receives an appropriate ultrasonic trigger signal from an ultrasonic reader, the tag responds in kind by powering up its ultrasonic emitter and transmitting its modulated data from the emitter.
A problem arises in the case where a tagged product is moved. The system that inventories these products will not know that the tagged product has been moved until the next time the reader tries to read the tag. Moreover, the reading range of ultrasonic tags is relatively low and, if the product has been moved far enough away, the system will not know where the product is, and will not know which local tag reader to trigger in order to locate the tagged product.
Accordingly, there is a need for a technique for detecting the movement of ultrasonic data tags.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.